1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to a system and method for implementing handoffs between heterogeneous networks using different communication schemes.
2. Description of the Related Art
With the drastic development of mobile communication technology, mobile communication services are being provided in a variety of schemes. A new mobile communication scheme is first deployed only in a trial network. When a mobile subscriber moves out of the trial network, he can continue his communication without interruption only if a handoff is performed between the new communication scheme-based network and an existing mobile communication network. If the handoff is not available, the communication service is discontinued.
An example of a new mobile communication scheme is a third-generation (3G) mobile communication system, WCDMA (Wideband Code Division Multiple Access) and an existing mobile communication scheme is a second-generation (2G) mobile communication system, CDMA (Code Division Multiple Access). The heterogeneous mobile communication networks will be described below with reference to FIG. 1.
FIG. 1 schematically illustrates a conventional mobile communication system. Referring to FIG. 1, a WCDMA network 100 includes a UE (User Equipment, i.e., a WCDMA telephone) 111 for receiving a communication service in WCDMA, a Node B 113, an RNC (Radio Network Controller) 115, and a UMSC (UMTS Mobile Switching Center) 117. The RNC 115, connected to a core network (CN: not shown), controls all processing related with connection to the UE 111 and radio resource assignment to UEs connected to the Node B 113. The Node B 113 controls channel assignment to the UE 111 in a physical layer.
A CDMA network 150 includes an MS (Mobile Station, i.e., a CDMA telephone) 151 for receiving a communication service in CDMA, a BTS (Base Transceiver Subsystem) 153, a BSC (Base Station Controller) 155, and an MSC 157. The BTS 153, BSC 155, and MSC 157 function in the same manner as the Node B 113, the RNC 115, and the UMSC 117, respectively.
When the UE 111 enters the service area of the CDMA network 150 during a communication service from the WCDMA network 100, a handoff is required to continue the communication service, but is not available.
The followings factors must be considered in order to support the handoff between the WCDMA network 100 and the CDMA network 150.
1. If a typical DBDM (Dual Band Dual Mode) terminal is used:
(1) the DBDM terminal must report the PN (Pseudorandom Noise) offset of a target system, that is, the CDMA network 150 to the CN;
(2) the DBDM terminal must report the RTD (Round Time Delay) of the target system to the CN;
(3) the DBDM terminal must synchronize its timing to the CDMA network 150 when a Handoff from a UMTS Command message is received from the WCDMA network 100; and
(4) the DBDM terminal must notify the WCDMA network 100 of its 32-bit ESN (Electronic Serial Number).
2. Radio resource information to be transmitted between MAPs (Mobile Application Parts) in heterogeneous networks: the UMSC 117 must transmit the following information to the MSC 157, and since a UMTS MAP supports this information, some parameters are changed in the 3G MAP and interface 1u-1/F.
(1) Service option;
(2) CDMA frequency;
(3) Frame offset;
(4) Code channel;
(5) Cell ID;
(6) RTD; and
(7) ESN.
3. Additional information to be formed in the RNC: the WCDMA communication system must have the following information about the 2G network as neighbor information.
(1) PN offset;
(2) MSC ID;
(3) BSC ID;
(4) BTS ID;
(5) Sector ID; and
(6) FA (Frequency Allocation) information.
To take the above considerations into account, actual air interface standards must also be changed. Thus, currently, the handoff is impossible.